1. Field of the Invention
This invention pertains generally to flow diverters, and more particularly to thin-film flow diverters for treatment of vascular diseases.
2. Description of Related Art
Conventional stent structures do not provide sufficient flow diversion to treat aneurysms. Ultra-low porous graft membrane such as ePTFE or Dacron polyester are too bulky and thrombogenic to be appropriate for use in the treatment of aneurysms in small vessels (e.g. vessels less than 5 mm in diameter, including neurovascular and peripheral arterial circulation) but have been successful in flow diversion in larger vessels (e.g. abdominal and thoracic aortic aneurysms).
PTFE, Dacron and other polymer structures are fabricated in such a fashion that it is extremely difficult to precisely control the porosity to a tolerance of 1 micron. Even in cases where porosity can macroscopically be controlled in these materials, specific shapes and distributions cannot be generated precisely. For example, it is highly difficult, if not impossible, to specifically fabricate a circular or diamond shape pattern that is regular and repeating into structures comprising these materials. In addition, ePTFE and Dacron are also very thick relative to thin films (on the order of 100 microns thick). This increases the size of any flow diversion device without providing significant benefit in regards to the thickness direction.
In many flow diverter applications, complete occlusion of the vessel's anomaly is unnecessary, and only partial occlusion is generally desired or warranted. Previous teachings of using deployable stents indicate for neurovascular applications the coverage area of the aneurysm sac must be at least 30%. These studies use large size holes (relative to the dimension of blood products) for evaluation.
Current approaches to prevent aneurysms from rupturing include both surgical and transcatheter methods. A surgical approach to treat aneurysms by “clipping” the aneurysm neck was developed by Dandy in 1936 and proved to be an effective treatment for a select group of aneurysms. However, this procedure requires a craniotomy (an opening in the skull) and is not always applicable depending on the aneurysm size, location, and complexity.
More recently, transcatheter procedures to treat vascular aneurysms have been developed. An endovascular therapy using platinum coils to fill the aneurysm sac was introduced in 1990. Because this coil embolization technique is less invasive and more cost effective than surgery, it has become the standard of care for most aneurysms. These coils pack the aneurysm sac densely to limit blood flow in the aneurysm and produce more local thrombosis within the aneurysm. While coils are beneficial, they can only be used for aneurysms with “necks” narrow enough to hold coils in the aneurysm. To address this issue, a stent can be placed across the neck of a broad-neck aneurysm and coils placed into the aneurysm through the cells of the stent. This procedure is complicated (it involves two types of devices: a stent and multiple coils), sometimes does not produce aneurysm occlusion, and is limited by the physical size of the stent's delivery system. The ideal device for treatment of aneurysms would be a “covered” stent, which occludes the neck of both narrow and broad necked aneurysms.
“Covered stents” have traditionally been conventional mesh type stents wrapped in expanded polytetrafluoroethylene (ePTFE). While they can wall off aneurysms by circumferentially covering the wall of an artery, they have been far too bulky for use as neurovascular stents or in other flow diversion vascular systems requiring a low profile. A low profile covered stent for the treatment of aneurysms in small, tortuous vessels has yet to be fully evaluated in vivo or in vitro.
Therefore, an object of the present invention is production and use of a thin-film structure (e.g. 1-10 microns) that can be patterned with specific shapes with a relatively high tolerance level (e.g. 1 micron or less).
Another object is to decrease the percent coverage of the material deployed over an aneurism sac by reducing the size of the fenestration.
A further object is a thin-film manufacturing process to enable a wide range of different shapes and distributions to be manufactured onto a single vascular flow diverter.
Another object is to provide a surface treatment to the thin-film that produces a rapid clotting cascade preventing flow into the aneurysm sac. At least some of these objectives will be met in the description provided below.